What is the first law of thermodynamics and what are some examples?

The first law of thermodynamics, also known as the law of conservation of energy, is a fundamental principle in physics that governs the behavior of energy within a system. Here are the key points and some everyday examples:

Statement of the First Law

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. For an isolated system, the total energy remains constant, although it can change forms such as from kinetic energy to potential energy, or from heat to work134.

Mathematical Representation

The law can be expressed mathematically as: [ \Delta U = Q - W ] or alternatively, [ \Delta U = q + W ] where:

• (\Delta U) is the change in internal energy of the system.
• (Q) (or (q)) is the heat supplied to the system.
• (W) is the work done by the system on its surroundings145.

Everyday Examples

1. Melting of Ice Cubes

When an ice cube is left out in the open, it absorbs heat from the surrounding air and melts into water. Here, the heat energy from the air is converted into the internal energy of the ice, causing it to change state from solid to liquid23.

2. Taking a Bath

When you take a bath, the heat from the warm water is transferred to your body, causing your body temperature to rise. Over time, the heat from the water is lost to the atmosphere, and your body's internal mechanisms help maintain its temperature. This process involves the transfer of heat energy from the water to your body and then to the surroundings2.

3. Photosynthesis

Plants use solar energy from the sun and convert it into chemical energy through photosynthesis. This process also produces oxygen as a byproduct. Here, solar energy is transformed into chemical energy, illustrating the conversion of one form of energy into another2.

4. Heat Engines

In a car engine or a power plant, chemical energy from fuel is converted into mechanical energy (work) and heat. The efficiency of these engines is based on the principle that the energy input (fuel) must equal the energy output (work and heat), highlighting the conservation of energy34.

5. Home Heating and Cooling

When you heat or cool a room, you are transferring energy from one place to another. For example, a heater converts electrical energy into heat energy, warming the room, while an air conditioner transfers heat energy from the room to the outside environment3.

These examples illustrate how the first law of thermodynamics is a pervasive principle that governs various processes in our daily lives.